<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.14/dist/vue.js"></script>
    <title>天气切换</title>
</head>

<body>
    <div id="root">
        <h2>今天天气很{{info}}</h2>
        <button @click="changeWeather"> 切换天气</button>
    </div>
    <script>
        const vm=new Vue({
            el: "#root",
            data: {
                isHot: true
            },
            computed: {
                info() {
                    return this.isHot ? '炎热' : '凉爽'
                }
            },
            methods: {
                changeWeather() {
                    this.isHot = !this.isHot
                }
            },
            /* watch:{
                isHot:{
                    immediate:true,//初始化时让handler调用一下
                    //当isHot发生改变时调用
                    handler(newValue,oldValue){
                        console.log('isHot被改变了',newValue,oldValue);
                    }
                }
            } */

        })
        vm.$watch('isHot', {
            immediate: true, //初始化时让handler调用一下
            //当isHot发生改变时调用
            handler(newValue, oldValue) {
                console.log('isHot被改变了', newValue, oldValue);
            }
        })
    </script>
</body>

</html>